Academic journal article Journal of Environmental Health

Management of Individual Mechanical Sewage-Treatment Systems: How Much Is Needed?

Academic journal article Journal of Environmental Health

Management of Individual Mechanical Sewage-Treatment Systems: How Much Is Needed?

Article excerpt


Over 2,600 individual mechanical sewage-treatment systems were studied to determine if mandatory maintenance contracts and semiannual inspections with effluent sample collection are adequate to meet discharge standards. The following discharge standards were set: 20 milligrams per liter (mg/L) for five-day biochemical oxygen demand ([BOD.sub.5]), 20 mg/L for total suspended solids (TSS), and 400 organisms per 100 milliliters for fecal coliform bacteria. In 1997, 67 percent of the individual mechanical sewage-treatment systems discharging in Will County, Illinois, were in violation of at least one discharge standard. The overall cost of management, shared by the homeowners and the county health department, ranged from $350 to $725 per year,


Millions of homes in the United States are constructed in rural areas beyond the reach of city sewers. Traditionally, homes in rural areas have used septic systems to treat and dispose of wastewater. Beginning in the 1970s, it was recognized that soil conditions in many rural areas are not suited to wastewater treatment, and that those conditions called for alternative methods of on-site wastewater treatment and disposal.

One technology emerged to meet this need. Known as home aerobic units or individual mechanical sewage treatment systems, these small versions of mechanical treatment plants are manufactured and sold by dozens of U.S. companies.

In the late 1970s, however, concerns surfaced about how well these units performed and how much maintenance was necessary. One early study evaluated the use of 36 individual mechanical sewage treatment systems in Boyd County, Kentucky (Waldorf, 1977). A licensed sewage treatment plant operator was hired to monitor, service and test all equipment. In the first five months of the project, nine of the electric pumps malfunctioned and had to be replaced. The study's author concluded that engineers and con tractors were not yet familiar with the systems and that a wide variety of installation problems were resulting (Waldorf, 1977).

A survey of 54 household aerobic sewage-treatment units was conducted in Preble County, Ohio, in the 1970s (Brewer, Lucas, & Prascak, 1978). Visual inspection found that 41 percent of the systems examined had black, odorous, or turbid effluent. Ten of the systems were sampled for chemical and bio logical analysis. The five-day biochemical oxygen demand ([BOD.sub.5]) of the effluents ranged from 9 to 79.5 milligrams per liter (mg/L) with an average of 30.9 mg/L. Total suspended solids (TSS) ranged from 5.5 to 164 mg/L with an average of 49.2 mg/L. Fecal coliform bacteria were present in all effluent samples, in concentrations ranging from 35 to 160 organisms per 100 milliliters (mL). Because ammonia is toxic to aquatic life, Brewer et al. also measured ammonia in the effluents and found concentrations that ranged from 7.5 to 94 mg/L with an average of 40.6 mg/L. Physical inspection of the systems, which ranged in age from one to eight years, showed that nearly one-third had at least one mechanical component that was not functioning (Brewer et al., 1978).

Hutzler, Fancy, and Waldorf (1978) summarized many early studies of individual mechanical sewage treatment systems. Table 1 gives the BOD, and TSS findings for over 1,000 samples taken for six previous studies. Hutzler et al. identified maintenance costs for individual mechanical sewage treatment systems ranging from $65 to $160 per year.

Otis and Boyle (1976) evaluated the designs of three individual mechanical sewage-treatment systems. They recommended regular maintenance with inspections at least every two months and suggested sludge removal every eight to 12 months.

Fancy (1980) examined the service records for 22 home aerobic units. He found that the oldest units (five to eight years old) had the highest maintenance costs, averaging $212 per year. The newer units (three to six years old) had an average maintenance cost of $160. …

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